The invention relates to electric fuses and a method for fixing a first part of a fuse made from metal or a ceramic material to a second part of the fuse made from metal or a ceramic material in the manufacture of electric fuses, more particularly, the present invention relates to appliance fuses and a connection formed of sintered material positioned between two parts made from different materials for producing a blowout fuse.
In the sense of the invention, the term "ceramic material" covers all ceramics, as well as metal and glass ceramics and also glasses.
The method extends the group of connecting and fixing processes known in the field of electric fuse manufacturing. Hitherto, nonmetallic parts such as glasses could be bonded together or joined in a partly melted state. Ceramic materials and glass ceramics could be assembled in a moist state and then jointly baked. In addition, solder glass could be used for joining together parts having rough surfaces.
Numerous methods are known in the manufacture of electric fuses for fixing two metallic parts. They differ through the temperature range at which the fixing process takes place. Thus, processes such as adhering, bonding, clamping, etc. are carried out at normal ambient temperatures, whereas when welding together two materials, very high temperatures are necessary. The two metallic parts can also be jointed by an additional material, such as e.g., in adhesion, a conductive adhesive at normal temperatures or a solder at greatly increased temperatures.
Most of the aforementioned methods cannot be used when joining metals to non-metals and specifically when fixing a metallic or metal-containing material to a ceramic material.
Fastenings of this type, inter alia, play a major part in the manufacture of electric fuses using so-called thick film technology. In thick film technology, complete circuits are produced on a ceramic substrate. For this purpose, electric contacts, conductors and resistance layers are applied to a ceramic substrate. Also, prefabricated components or subassemblies are integrated into the circuit as SMD elements. For this purpose, the necessary contact points, conductors and resistors are applied to the ceramic surface as pulverulent layers of metal-containing mixtures. This can also take place in the form of pastes, which carry the same material mixture as an emulsion. The permanent fixing of the very fine-grained materials takes place by firing. Firing is a process in which all the components of the applied fine-grained mass are interconnected. As a function of the composition of the mixtures, this takes place at or above 800.degree. C. The procedure involving the application of pastes and firing can be repeated. In successive stages it is possible to form complex structures on the substrate. Only subsequently in a further manufacturing step are components soldered to the contacts, which cannot be exposed to the elevated temperatures of the firing process, such as e.g. transistors.
In the manufacture of electric fuses in thick film technology, the metal mixtures are applied in the same way to the ends or terminal edges of ceramic substrates. As with fuses, the fuse element can be subsequently applied to the ceramic support in the form of a further layer between the contacts. Particularly in the overload range of the fuse, this structure leads to an intense heat dissipation from the fuse element of the fuse to the support material. This heat dissipation is detrimental to the function of the component as a fuse.
From the thermal insulation standpoint, a fuse element in air or inert gas is more favorable for the structure of a fuse. In this case, for example, a first fuse ceramic substrate in the form of a support and a second ceramic substrate serving as a cover are metallized by firing a paste. This produces electric contacts at remote ends of the substrates. A wire is fixed between the two contacts for acting as the fuse element. This arrangement is permanently interconnected by adhesion. A reliable electrical connection of the contacts to one another and to the fuse element takes place in a subsequent working stage by soldering.
Thus, hitherto, for the manufacture of blowout fuses it has always been necessary to have a multistage operating procedure. Examples for possible manufacturing methods are given in German utility model 94 07 550.6. One of these methods is based on half-shells, whose ends are metallized and between which the fuse element is fixed to both halves by adhesion. The fuse is assembled by adhesion or clamping. In a subsequent stage, soldering produces a reliable electrical contact between the metallizations serving as contact points and the fuse element. Thus, this production method for the mechanical fixing and electrical connection involves several working stages, such as the metallization of the ends of the half-shells and the soldering, both being heat processes involving relatively high temperatures. Adhesion and bonding constitutes auxiliary processes requiring additional materials that are not necessary for the function of the fuse.
All the other hitherto known methods for the manufacture of electric fuses, particularly appliance fuses made from one or two ceramic or glass bodies or using metal caps at the ends require numerous individual, successively performed stages for fixing the components.
Therefore the problem arises of providing a method usable in the manufacture of electric fuses for the reliable mechanical fixing of a first part made from metal or a ceramic material to a second part made from metal or a ceramic material.